This invention relates to sewing machines and in particular to presser bar mechanisms therefor.
Sewing machines that are intended for use in mending, darning, and embroidery applications, or the like, require that the pressure exerted by the presser foot on the work piece be reduced to near zero while maintaining the presser foot in contact with the work piece. This allows complete freedom of movement when feeding the work piece while, at the same time, maintaining the work piece in contact with the work supporting surface to prevent flagging.
Prior art devices accomplish this generally by means of a counter balance spring arranged in opposition to the spring that urges the presser bar downwardly toward the work piece. See, for example, U.S. Pat. No. 3,329,115, issued July 4, 1967 to Ciecior. Such devices, however, have no convenient way to disengage the counter balance spring when it is desired to resume normal sewing. Other prior art devices, such as that disclosed in U.S. Pat. No. 3,294,047, issued Dec. 27, 1966 to Graham, disengage the primary spring that urges the presser bar downwardly for normal sewing but permits a secondary spring that also urges the presser bar downwardly, but with a lighter pressure, to control the pressure exerted by the presser foot on the work piece. This construction, however, results in a complex mechanism that is costly to manufacture and maintain.
It is therefore an object of this invention to provide a reliable device that is inexpensive to manufacture for counter balancing the effect of the presser bar biasing spring.
It is another objective of this invention to provide a means for easily engaging and disengaging the counter balancing device.
Other objects and advantages of the invention will become apparent through reference to the accompanying drawings and descriptive matter which illustrate a preferred embodiment of this invention.